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6 - Star Birth

6 - Star Birth. Our Galaxy. side “view”. mean density ~1 cm -3 By number: ~90% H ~10% He <1% everything else (mostly O, C, N, Ne). top “view”. Photon-Atom Interactions.  = 21 cm. N. N. N. N. 21-cm H emission line. Atoms versus Dust. only specific wavelengths absorbed. GAS.

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6 - Star Birth

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  1. 6 - Star Birth

  2. Our Galaxy side “view” mean density ~1 cm-3 By number: ~90% H ~10% He <1% everything else (mostly O, C, N, Ne) top “view”

  3. Photon-Atom Interactions  = 21 cm N N N N 21-cm H emission line

  4. Atoms versus Dust only specific wavelengths absorbed GAS all wavelengths affected - shorter ones more than longer ones DUST

  5. Interstellar Extinction & Reddening visible light only visible - infrared light

  6. DUST • Solid Grains  C, Si, O, + …? T≤ 1200 K • Absorb & Scatter starlight • Polarization  Transmission & Scattering • Thermal Emission dust emission versus blackbody conservation of energy absorbed energy must be released

  7. Molecules in the ISM pretty picture from Ehrenfreund & Charnley 2000 ARAA 38, 427

  8. Giant Molecular Clouds Mass ~ 104-107 M Size ~ 20-80 pc Density ~ 200-106 cm-3 Temperature ~ 10 K Composition: H2, CO, Dust, .. visible to human vision invisible to human vision

  9. H C N O some specific examples H2 hydrogen CO carbon monoxide H2O water H2CO formaldehyde C3H2 cyclopropenylidene HC11N cyanodecapentayn

  10. Polycyclic Aromatic Hydrocarbons (PAHs) (ISM & Auto Exhaust!) C6H6 - benzene C24H12 - coronene (H atoms not shown) (no perfect fit to data, yet…)

  11. where are the complex silicon-based molecules? Ehrenfreund & Charnley 2000

  12. so far, only in the minds of fiction writers….. Ehrenfreund & Charnley 2000

  13. The World of Sir Fred (Hoyle & Wickramasinghe) Wickramasinge - first large compendium of light scattering by small particles Hoyle - He  C fusion, essential to existence of life! Together: interstellar dust grains are (basically) freeze-dried bacteria “bug”-carrying comets cause outbreaks of influenza* *we will come back to the concept of panspermia later on

  14. The Case of the Missing Tryptophan 1983-1984 “We detect feature due to interstellar tryptophan..” “You detected an instrumental artifact of the detector. In properly exposed images, the ‘feature’ isn’t there..” “But, but…”

  15. Birth of Stars & Planetary Systems Cloud Collapse - occurs deep in cloud

  16. Some young disks & jets revealed

  17. “proplyds” (protoplanetary disks) seen in star-forming regions

  18. Older “Debris Disks”

  19. other disks are like ours was in its youth

  20. Formation of planetary systems…

  21. We will return to this topic when we look at the formation of our own solar system

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